The three stage vacuum pump, and alternatively expander, relate generally to devices that alter or reduce the pressure of gases within a container, typically to very low vacuums or alternatively produce power as a gas expands. More specifically, these devices refer to multiple stages of scrolls that greatly increase the vacuums obtained during usage.
A unique aspect of the present disclosure is a three stage pump using various arrangements of scrolls that achieves vacuums of approximately 2 mt, that is, two millitorr (mTorr). These high vacuums apply to compact equipment such as portable mass spectrometers.
Scroll devices have been used as compressors and vacuum pumps for many years. In general, they have been limited to a single stage of compression due to the complexity of two or more stages. In a single stage, a spiral involute or scroll upon a rotating plate orbits within a fixed spiral or scroll upon a stationery plate. A motor shaft turns a shaft that orbits a scroll eccentrically within a fixed scroll. The eccentric orbit forces a gas through and out of the fixed scroll thus creating a vacuum in a container in communication with the fixed scroll. An expander operates with the same principle only turning the scrolls in reverse. When referring to compressors, it is understood that a vacuum pump can be substituted for compressor and that an expander can be an alternate usage when the scrolls operate in reverse from an expanding gas.
Often oil is used during manufacture and operation of compressors. Oil free or oil less scroll type compressors and vacuum pumps have difficult and expensive manufacturing, due to the high precision of the scroll in each compressor and pump. For oil lubricated equipment, swing links often minimize the leakage from gaps in the scrolls by allowing the scrolls to contact the plate of the scroll. Such links cannot be used in an oil free piece of equipment because of the friction and wear upon the scrolls. If the fixed and orbiting scrolls in oil free equipment lack precision, leakage will occur and the equipment performance will decline as vacuums take longer to induce or do not arise at all.
Prior art designs have previously improved vacuum pumps, particularly the tips of the scrolls. In the preceding work of this inventor, U.S. Pat. No. 6,511,308, a sealant is applied to the two stage scrolls during manufacturing. The pump with the sealant upon the scrolls is then operated which distributes the sealant between the scrolls. The pump is then disassembled to let the sealant cure. After curing the sealant, the pump is reassembled for use. During use, this patented pump only achieves a vacuum on the order of 100 mt.
U.S. Pat. No. 3,802,809, which issued to Vulliez, disclosed a pump having a scroll orbiting within a fixed scroll. Beneath the fixed disk, a bellows guides the gases evacuated from a container. The bellows spans between the involute and the housing, nearly the height of the pump. This pump and many others are cooled by ambient air in the vicinity of the pump.
In some applications, scroll type vacuum pumps have notoriety for achieving high vacuums. A few large scroll vacuum pumps can achieve vacuums as high as 50 mt. However, industry, science, and research still demand compact vacuum pumps that can achieve higher vacuums.
The present disclosure overcomes the limitations of the prior art where a need exists for higher vacuums in equipment of compact form. That is, the art of the present disclosure, a three stage scroll vacuum pump utilizes a magnetic coupling for power transfer and fins upon the orbiting scroll and inside the housing for heat transfer, both without leakage of the working fluid.